If we can't get in contact directly with any of the aliens that might live on the Milky Way's billions and billions of planets, then the next best option is to look for evidence that they have reshaped their worlds. And silly as it might sound, our best hope is that aliens use hairspray and central air.

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The underlying reason for that is simple enough — the chemicals on Earth once used in those products were known as chlorofluorocarbons, or CFCs. The reason we stopped using CFCs is that they're extremely strong greenhouse gases and played a major role in the depletion of the ozone layer. But because CFCs are non-toxic chemicals, it wouldn't be surprising for another alien civilization to make the same mistake we did and use such chemicals in their products.

If an alien world did make use of CFCs, the evidence would quickly show up in that planet's atmosphere — after all, less than a century's worth of CFC use on Earth radically affected our planet's atmosphere. Crucially, chlorofluorocarbons don't occur naturally under any known circumstances, so if we detected the presence of CFCs in the atmosphere of another planet, it would almost certainly be proof that an intelligent species had synthesized and used them. Best of all, the chemical signatures of CFCs are radically different from those of naturally occuring chemicals, so we shouldn't need too much of a technological boost before we should be able to detect them.

"An industrialized civilization will be one that will use its planetary resources for fabrication, the soon-to-be-detectable-from-Earth atmospheric byproducts of which could be a tell-tale sign of their activity. We are on the scientific verge of being able to actively look for extrasolar worlds inhabited by technological civilizations. We are about a decade away of being able to measure detailed compositions of the atmospheres of extrasolar planets."

Som and his colleagues are currently hoping to raise the quite reasonable sum of $24,000 to continue their research into the detection of artificial chemical signatures on far distant alien worlds. One particularly intriguing wrinkle for the project is the possibility that alien use of CFCs and other artificial chemicals could be used to warm up and terraform planets that would not otherwise be livable, meaning we could detect such chemicals on inhabited planets that lie outside stars' usual habitable zone. Som explains:

"Artificially warming a body outside of the habitable zone to make it habitable could also be a tell-tale sign of intelligence. For example, suppose that in a few thousand years, humans have terraformed Mars. Suppose that an alien species is observing our solar system and finds Earth. In addition, it measures the atmospheric composition of Mars, a planet essentially outside the habitable zone of our sun, and finds elevated greenhouses gasses in addition to water vapor and oxygen. This two-planet system would be a strong indication to them of an intelligent civilization at work expanding its cradle outside of its home planet."